Apparatus for completing wells



Dec. 7, 1954 c. R. FAST 2,696,260

APPARATUS FOR COMPLETING WELLS original Filed June 13, 195o I7/ FIG. 2

CLARENCE R. FAST ,JNVENTOR BY 1 a l ATTORNEY United States Patent Office2,696,260 Patented Dec. 7, 1954 APPARATUS FOR CMPLETING WELLS ClarenceR. Fast, Tulsa, kla., assignor to Stanolind Oil and Gas Company, Tulsa,Okla., a corporation of Delaware Uriginal appiieation .lune 13, 1950,Serial No. 167,809. Divided and this application May 7, 1951, Serial No.225,026

7 Claims. (Cl. 166--65) This invention pertains to an improved apparatusfor treating weils. More particularly, this invention pertains to animprovement in apparatus for producing a fracture in a formationpenetrated by a well to facilitate the recovery of tiuids therefrom.This is a division of my copending application Serial Number 167,809,led June 13, 1950.

Various methods have been proposed for increasing the productivity ofwater, oil, and gas wells; for example, nitroglycerin has been detonatedin a Well in some cases either to enlarge the well diameter or tofracture the formations immediately adjacent the well. Acid has beeninjected into wells and into formations, particularly calcareousformations, for the same purpose. Wells have also been drilled laterallyfrom a central bore for the purpose of increasing the productivity anddrainage area of wells. Fractures have also been produced in formationsby the application of a high hydrostatic pressure in the well, wherebythe permeability of a formation adjacent a well and the drainage areaaround the well are increased.

lt is an object of this` invention to provide an improved wellapparatus. A further object of this invention is to provide an improvedapparatus for solidifying a magnetic duid in a well. These and otherobjects of this invention will become more apparent from the followingdescription in which reference will be made to the accompanyingdrawings. In these drawings:

Figure l is a diagrammatic representation of a cross section of a wellshowing apparatus employed to fracture a formation in accordance withthis invention; and

Figure 2 is a cross sectional View of one type of apparatus used inisolating a formation to be fractured and at the same time changing theproperties of the fracturing tiuid so that it has a more desirablefiltrate rate.

The present improvement in the process of fracturing formationsconsists, in brief, of temporarily isolating a formation by magneticmeans and injecting a fracturing liquid into it under a pressure greatenough to produce a fracture. As indicated in Figure l, a well 10 may beequipped with a tubing ll, which has associated therewith, atapproximately the depth of the formation which is to be fractured, amagnet 12. At the surface a highpressure, high-volume pump 13 isconnected to the upper end of the tubing, and the suction line of thispump may be, in turn, connected to a source of magnetic fluid or otherfracturing liquid. the preferred embodiment, an electromagnet, leads 14from the surface to the electromagnet may be attached as by clips to thetubing ll. At the surface these leads are connected across battery 15 orother suitable supply of electric energy. Obviously, this power sourcemay be a DC or an AC generator, or any supply which will produce amagnetic field about an electromagnetic coil, as is well known in theart. A switch 16 may also be incorporated in the circuit of theelectromagnetic coil.

A fluid which has the property of stiffening when it is in a magaeticfield is prepared at the surface. This fluid, herein referred to as amagnetic fluid, is defined as a duid containing finely divided magneticmaterials wherein the frictional forces between the magnetic materialscan be controlled by the application of a magnetic field. Besides thismagnetic material, the magnetic uid contains a suspending liquid. In thecase where an oil-producing formation is to be fractured, the liquidcomponent of the magnetic fluid is preferably oily. Any mineral oil,fish oil, animal oil, or other oil-miscible liquid can vbe used.

ln case the magnet 12 is, as in A trixotropic oil-i. e., an oil whichhas appreciable gel strength-is sometimes desirable to prevent themagnetic particles from settling when the fluid is in a quiescentunmagnetized state. Addition of a small amount of a highly polarsurface-active agent, such as oleic acid, to the oil produces thiseffect. Crude oil from the formation itself can be used; but, ingeneral, I have found that more viscous oils are generally desirable.Whereas crude oil may have a viscosity of from about 1 to about l()centipoises, a viscosity 200 or more centipoises has been found to bemore desirable. A lubricating oil, a steam cylinder oil, or the like areexamples of the preferred oily liquid for the magnetic fluid. In case ofa water-producing or water-disposal formation, an aqueous base liquid ispreferred. I incorporate in this liquid the finely divided, highlypenneable magnetic solid. Suitable solids are hydrogenreduced iron,hypo-eutectoid steels, eutectic steels, hypereutectoid steels, carbonyliron, carbon steels, and magnetic iron oxide. Other finely dividedmaterials which exhibit .magnetic properties, for example, cobalt,nickel, and molybdenum powders, may be used in place of the ironpowders; but, in general, these particles have a lower permeability thanthe iron powders and, therefore, are less desirable.

The magnetic material is ground to a particle size of between about 1/2and about 60 microns, or more. In general, the larger particle sizes arepreferred, since the permeability of a mixture of this material with aliquid is directly proportional to the particle size. The limitingfactor on maximum particle size is the ability to maintain the particlessuspensionthe more viscous the suspending liquid, the larger theparticles it will suspend.

The ratio of magnetic material to liquid may be varied over asubstantial range. I have found, however, that the ratio of from about lto about 10 parts magnetic material to l part of liquid by weightproduces satisfactory fracturing liquids. Since the permeability of thefluid increases with an increase in the ratio of magnetic material toliquid, higher ratios of magnetic material to liquid are preferred.Pumpability of the magnetic fluid fracturing liquid appears to be theonly factor which limits the maximum ratio of magnetic material toliquid, and pumpability of the uid depends, among other things, upon thepump, the particle size, the liquid, and the like. There appears to beno minimum concentration of magnetic material in the oil except that atlow concentrations the permeability of the magnetic fluid becomesrelativeiy low, thereby decreasing the viscosity of the fluid under amagnetic field. A ratio of magnetic material to liquid of greater thanabout 5 is preferred. The permeability of the magnetic fluid isgenerally the element which determines the minimum concentration ofmagnetic material in the liquid. A permeability of greater than about 3in CGS units is considered operable in most cases; however, I prefer apermeability of greater than about 5. The ratio of magnetic material toliquid must, therefore, be adjusted for each set of circumstances.

These particles are incorporated in the suitable means; for example, bystirring mixer. This magnetic duid through tubing Il by pump clusion ofthe iron particles,

liquid by any or by a jet-type is displaced into the Well lll 13. Thefluid, due to the inis generally more dense than the weil fluid and,therefore, unless otherwise constrained, appears to displace the wellduids upwardly in the well. The magnetic iiuid may be placed in the wellbefore the magnet 12 is lowered into the well or, in the case of anelectromagnet, before it is energized. I have found it generallydesirable, however, to energize the magnet before the magnetic fluid isintroduced into the well to prevent loss of the magnetic fluid to theformations. Where the core of an electromagnet is highly permeable, as,for example, where the core is constructed of tubular magnetic materialsuch as iron, the magnetic field within the core is substantially zeroand, therefore, the flow of the magnetic material through the core isnot materially retarded by the magnet. Near the end of the magneticcoil, which is preferably placed near the end of the tubing, themagnetic field Vhas its maximum intensity. Therefore, the frictionalforces between the magnetic particles, i. e., the

in the range of from about 20 to about Y viscosity of the magneticfluid, are greatest around the end of the tubing. The extreme viscosityor set of the magnetic fluid prevents the magnetic fluid from flowingupwardly around the tubing-the viscous fluid in this region functioninglike a packer between the tubing and the well wall. This high viscosityis generally adequate to prevent flow of the magnetic fluid into theannulus between the tubing and the well wall, but a packer mayoccasionally be set in this area to advantage. Magnet1c fluid issuingfrom the tubing is by comparison substantially less viscous than themagnetic fluid between the tubing and the well walls. Accordingly, thismagnetic fluid flows into and fills the confined zone in the Well belowthe end of the tubing. The zone may be limited at the lower end by thebottom of the well, by a packer, a plug, another magnet, or other meanswell known in this art. The magnetic field from magnet l2 extends intothis fluid 'and thereby increases its viscosity. This increasedviscosity prevents the magnetic fluid from penetrating the pores of theformation.

lf injection of the fluid is continued after the confined zone becomesfilled with viscous magnetic fluid, hydraulic pressure on the fluidrises until the strength of the formation is overcome and a fracture ll7results. The hydraulic pressure in the confined zone necessary toproduce a fracture has been found to vary in wells 2000 ft. or more indepth from about 0.7 to about l lb. per foot of well depth. Thispressure of the magnetic fluid required to fracture a formation ishereinafter referred to as the formationbreakdown pressure. It isgenerally recognized by an observation of the pressure in the tubing.After the confined zone becomes filled with magnetic fluid, the pressurerise, assuming a volume of two or more barrels per minute, is roughlyproportional to the volume of the fluid injected into the well. Afterthe formation fractures, the pressure rise ceases to be proportional tothe volume of the fluid injected into the well. In fact, in many cases,the pressure may decrease sharply when the formation fractures, eventhough there is no decrease in the fluid injection rate. The pressure atwhich this change in the slope of a pressure-versus-Volume curve occursis the formation-breakdown pressure. After the formation fractures, themagnetic fluid enters, and the fracture may be extended a substantialdistance from the well by continuing to pump uid into the well. Itappears that whereas the field strength of the magnet and the viscosityof the magnetic fluid are greatest adjacent the end of the magnet, theviscosity of the magnetic fluid may be maintained reasonably high for asubstantial distance into the formation due to the relatively highpermeability of the magnetic fluid in comparison to the permeability ofthe rocks. That is, the flux lines of the magnet appear to beconcentrated in and to follow the lens of magnetic material and toreturn to the tubing from great distances through the rocks. Obviously,the viscosity of the fluid gradually decreases with distance from themagnet as the field decreases. Once a fracture has been initiated, thepressure required to eX- tend it is generally reduced, and, therefore,the fracture appears to be extended several feet into the rocks, eventhough the flux density, and therefore the viscosity of the fluid, ismuch less at this distance than in the well at the end of the tubing.The flux density is generally maintained as high as possible in the wellconsistent with sound engineering design of permanent or electromagnetsso that the fracture can be extended to great distances.

Any amount of magnetic fluid may be injected into the fracture. Forexample, from about 100 to about 5000 gallons or more may be used, butit appears that a 1000- gallon treatment on the average is about themost desirable, considering cost and results.

After the magnetic fluid has been injected into the fracture to thedesired distance, the electromagnet may be deenergized by opening switch16. Any magnetic fluid in the well 10 and fracture 17 then becomes lessviscous, and the liquid filters into the formations surrounding thefracture, allowing the granular particles to be deposited in thefracture. These particles then support the overlying formations andmaintain a highly fluid-permeable path from the formation into the well.The liquid, being in the preferred embodiment miscible with the liquidin the formation, may then be produced with the well fluid, as byflowing, swabbing, or pumping the well.

The magnetic field may be produced, as indicated above, by a number oftypes of apparatus. In the case of an electromagnet, the magnetic fieldmay be produced or discontinued at will, whereas inthe case of apermanent magnet the magnetic field is continuous. An electromagnet is,therefore, preferred, since the removal of the tubing may be facilitatedby de-energizing the magnet and reducing the viscosity of the magneticfluid before removing the tubing. Even though the viscosity of themagnetic uid is not reduced, however, the tubing and magnet may beremoved from the well by the application of a suitable force. It appearsthat, upon the application of a magnetic field, the magnetic particlesin a magnetic fluid come into contact with each other, producing a quasirigid or very viscous connection between the magnet and the well walls,thereby tending to freeze the tubing in the well. The magnet can,however, be moved through this -viscous mass if sufficient force isapplied.

An alternative type of apparatus particularly adapted to fracturingformations is shown in Figure 2. In this embodiment, a non-magnetictubular sub 21 is attached to the lower end of tubing lll. Wherealternating current is applied to the magnetic coil 22 at the lower endof the sub, the sub is preferably constructed of a strong nonconductingmaterial such as plastic. However, where direct current is used toenergize the coil, the sub may be constructed of brass or othernonmagnetic metals. While the non-magnetic sub is obviously desirable,it is not necessary since it merely assists in concentrating themagnetic field from the coil. Coil 22 is connected via leads 14 to asource of electrical energy as above described. The coil is wound on amagnetic core 23 having upper annular pole piece 24 and lower annularpole piece 25. These pole pieces and the core may be laminated toadvantage where AC power is used. Lower pole piece 25 may be a circularplate which closes the lower end of the tubing. A number of fluidoutlets 26 are provided around the periphery of the tubular core andextending through the coil. These conduits may be threaded into thetubular core as indicated. They are preferably constructed of anon-magnetic material such as brass so as not to affect the magneticfield produced by the coil.

In operation, this apparatus is lowered into the well, as described inconnection with the embodiment shown in Figure l, the coil is energized,and the magnetic fluid is injected through tubing 1li, non-magnetic sub21, and fluid outlets 26 into the well. Since the magnetic field issubstantially stronger adjacent the pole pieces, the magnetic fluid inthe well contiguous to these pole pieces has a viscosity much greaterthan the viscosity of the magnetic fluid in the intermediate zone. Infact, the magnetic fluid adjacent the pole pieces may, with high fieldstrength, be made practically rigid, thereby preventing the escape ofmagnetic fluid into the well above and below the pole pieces. Beingrigid not only prevents flow of the magnetic fluid into the well aboveand below the coil but also prevents it from flowing into the formationat these po1nts. Since the reluctance of the flux path through theformation is roughly equal to the reluctance of an air path, themagnetic field between the pole pieces extends out from the coil throughthe formation, and the flux density decreases as a function of theradial distance from the pole pieces. The depth of penetration of theflux path into the formation is dependent on the ampere-turns in thecoil and on the length of the coil. Accordingly, high power input to thecoil and a long coil, e. g., from about 5 to 20 ft. or more, arepreferred. The viscosity of the magnetic fluid around the coil is thusincreased to some extent so that it does not readily penetrate thepermeable formations-the magnetic fluid in effect having a low filtraterate due to the forces between the magnetic particles in the liquid.Since the magnetic fluid in the zone surrounding the energized coil hasa low filtrate rate, it will not be lost into the formations when a highpressure is applied. This permits the formation-breakdown pressure to bebuilt up so that a fracture can be initiated.

The magnetic field from coil 22 extends into the formation a substantialdistance, the strength of this field, and accordingly the viscosity ofthe magnetic fluid, being a function of the distance. In some cases, themagnetic fluid enters the formation in a lens which is much closer toone pole piece than to the other so that the highly permeable pole pieceis, in effect, extended out into the formation by the relatively highpermeability magnetic fluid. The magnetic flux leaving one pole piecewould then extend in a concentrated path through this lens out into theformation and would return to the other pole piece through the highreluctance formation. Thus, by

the embodiment illustrated in Figure 2, an intermediate zone in a wellcan be isolated from the remainder of the well and the adjacentformation can be fractured by a simplified process, i. e., a processwhich avoids the use of packers, plugs, or the like that are alwaysdifiicult to set in a well and obtain a seal.

In some cases, it is desirable to use spaced magnets to isolate a zonerather than to isolate a zone between the pole pieces of a single magnetas above described. In such case the magnetic tield in the isolated zonebetween the magnets is subject to better control, and therefore theviscosity of the magnetic fluid in this zone is more easily controlled.

This invention has been described above with particular reference tofracturing a formation with the magnetic fluid which thus performs twofunctions-both isolating and fracturing a formation. In some cases, itis desirable to use different fluids for the two functions. That is, Ihave found it particularly advantageous to first surround the magnet ormagnets with magnetic fluid, stiften this iiuid at f points in the wellby energizing the magnet or magnets, and then inject a fracturing liquidinto the zone isolated by the magnetic fluid. The second or fracturingliquid may be any liquid which has a very low filtrate rate and whichwill thus not tilter into the formations too fast to permit theformation-breakdown pressure to develop. Suitable fracturing liquidssuch as oily materials containing bodying agents, for example, themetallic soaps, particularly the hydroxy aluminum soaps, are describedin the copending application of Joseph B. Clark, Serial Number 29,932,filed May 28, 1948.

It will thus be apparent that this invention is subject to a widevariety of embodiments and should, therefore, not be limited by theabove-mentioned apparatus or by the particular magnetic iiuidsdescribed. Instead this invention should be limited in scope only by theappended claims.

I claim:

1. A Well packer for isolating a section of a well including, a tubingstring in said well, a highly permeable tubular electromagnetic coreattached to the lower end of said tubing string, spaced annular polepieces on said core, an electromagnetic coil on said core between saidpole pieces, means to energize said electromagnetic coil, a radial uidpassage through said coil at a zone of relatively low flux densitybetween said pole pieces, and a plugging liquid containing a powderedmagnetic material, said plugging liquid being disposed around said polepieces and being substantially solidified when said electromagnetic coilis energized.

2. A well packer for isolating a section of a well comprising a welltubing in said well, a highly permeable tubular electromagnetic core insaid well, spaced annular pole pieces on said core, an electromagneticcoil on said core between said pole pieces, means to energize saidelectromagnetic coil, a radial fluid passage through said coil, andnon-magnetic tubular means to connect said core to said tubing.

3. A well packer for isolating a section of a well containing a welltubing including a highly permeable tubular electromagnetic core attubing, spaced annular pole pieces on said core, a source of electricenergy at the surface, an electromagnetic coil on said core between saidpole pieces, conductor means connecting said source of electric energyto said coil, and a radial uid passage through said coil at a zone ofrelatively low flux density.

4. A Well packer comprising an electromagnet disposed in a well, meansto energize said electromagnet, a magnetic uid comprising a liquidcontaining a magnetic material, said electromagnet being surrounded insaid well by said magnetic fluid, and said magnetic fluid being capableof substantial consolidation in said well by said electromagnet, and awell tubing connected to said electromagnet and extending between saidelectromagnet and the surface.

5. A well packer according to claim 4 wherein said means includes asource of electrical energy at the surface and an electrical conductorconnected between said source and said electromagnet.

6. A well packer for isolating a section of a well including a tubingstring in said well, a tubular magnetic core disposed at the lower endof said tubing string, spaced annular pole pieces on said magnet, aninsulated coil on said core between said pole pieces, and a radial fluidpassage through said coil between said pole pieces.

7. An apparatus for isolating and treating a section of a well includinga tubing string extending into said well, a highly permeable tubularelectromagnetic core at the lower end of said tubing, spaced annularpole pieces on said core, an electromagnetic coil on said core betweensaid pole pieces, a source of electrical energy at the surface,electrical conductor means affixed to said well tubing and connectedbetween said source and said coil, a radial uid passage through saidcoil between said pole pieces, a magnetic iiuid comprising a liquidcontaining a powdered magnetic material surrounding said pole pieces,and means to inject uid down said tubing and through said fluid passagefor treating said section of said Well.

the lower end of said well References Cited in the tile of this patentUNITED STATES PATENTS Number Name Date 1,529,570 Bethke Mar. l0, 19252,033,561 Wells Mar. l0, 1936 2,423,653 Lauman July 8, 1947 FOREIGNPATENTS Number Country Date 24,463 Norway Apr. 14, 1914 OTHER REFERENCESBureau of Standards Bulletin, June 1949, pages 74-76. (Copy in -21,Magnetic Fluids, Division 48.)

Journal of Applied Physics, vol. 20, December 1949, pages 1137-1140.(Copy in Patent Office Library.)

The Oil and Gas Journal, October 14, 1948, pages 76-78. (Copy in 166-21,Division 49.)

